In a double seaming apparatus, the intermediate seaming thickness at the end of first seaming (hereinafter referred to as the dimension Tc) or the seaming thickness of the final shape at the end of second seaming (hereinafter referred to as the dimension T) sometimes changes due to heat expansion resulting from an increase in temperature. This increase in temperature is caused by frictional heat or the like of the seaming rollers during the seaming work over a long period of time. To cope with this change or when the kind of can is changed, the displacements of a first seaming roller and a second seaming roller to the seaming chuck are controlled to adjust the seaming dimension. Generally, in adjusting the seaming dimension, the fixing angle of the individual seaming rollers to a roller fixing axis is finely hand adjusted by a skilled person. In order to accomplish the adjustment more simply, a method of simultaneously adjusting a plurality of rollers has been proposed.
Examples of the method of simultaneously adjusting the slippage of a plurality of seaming rollers hitherto proposed include a method of dividing a part of the double seaming cam and moving the divided portion in the radial direction, and a method of pivoting the seaming cam around a fulcrum to thereby effect movement in a horizontal direction as disclosed, for example, in JP-A-8-168837 and JP-A-8-197176 (the term "JPA" as used herein means an "unexamined published Japanese patent application").
In conventional methods of simultaneously adjusting the displacements of seaming rollers, for example, in the method of dividing a part of a double seaming cam and moving the boundary portion in the radial direction, when the divided part is shifted in the radial direction, a step is generated in the cam groove at the boundary portion between the fixed part and the divided part. The cam follower is shocked on passing the stepped portion and as a result, the seaming rollers are vibrated which can give rise to a seaming failure. Thus, this method is disadvantageous in that high-speed double seaming cannot be performed. The method of pivoting the seaming cam as a whole also presents a problem. That is, because the maximum displacement sections of the first and second seaming rollers are shifted together, the maximum displacement sections of the first and second seaming rollers cannot be individually adjusted.